In many integrated circuit fabrication processes, it can be difficult to maintain uniform conditions. As a result, integrated circuits from a fabrication process can have different electrical characteristics. Some integrated circuits may even differ from a desired target of an electrical specification. Accordingly, it can be beneficial if the integrated circuit contains a trimming circuit to adjust the electrical characteristics of the integrated circuit.
In some integrated circuits, including ROM-based devices, it can be difficult to store trimming related information because writing the trimming information into memory would use valuable memory slots. Other techniques of storing trimming related information have their own limitations. For example, floating gate cells are reliable but are expensive to make. Laser fuses can be used, but these fuses can be difficult to manufacture and test. Electrical fuses may also be used, but the state of an electrical fuse can be difficult to determine if the fuse is only partially blown. Accordingly, there is a need for a memory cell able to reliably store trimming related information, and that can be manufactured relatively inexpensively.